274 ANATOMY AND PHYSIOLOGY 



Animal Heat. An internal temperature of about 100 F. is 

 necessary to the normal activity of the body tissues. This, the 

 tissues themselves can accomplish with proper materials in the 

 form of food, and oxygen for the chemical work, the latter being 

 supplied in the air we breathe. 



The great source of animal heat is in the most active tissues 

 muscles and glands; the heat produced in these is equalized in 

 all tissues by the circulating fluids. 



The kind of food which is eaten has a direct effect upon the 

 production of heat; protein substances yield more than starchy 

 foods, while fats yield more than proteins and starches together. 



The ingestion of food causes a rise of temperature, due both to 

 the chemical and mechanical work of the digestive organs. This 

 rise is normal. 



As the body is continually generating heat so it is continually 

 losing it in various ways by radiation to the surrounding atmos- 

 phere, by conduction to the clothing, by evaporation from the 

 lungs and skin, etc., etc. 



In cold weather heat production is desired. This can be accom- 

 plished by selecting heat-generating foods, by taking hot foods and 

 by muscle exercise; the heat thus generated can be conserved by 

 clothing the body in materials which prevent radiation and con- 

 duction, as wool or silk. In hot weather heat production is to be 

 avoided and heat dissipation is sought; this is facilitated by the 

 selection of starchy and protein foods, taking cool drinks and wear- 

 ing lighter garments, as cotton or linen. 



For health and comfort it is necessary that a proper internal 

 relation be maintained between heat production and heat dissipation. 

 For this, the body possesses its own self-regulating mechanisms; 

 for ^example, muscle exercise produces heat, but the associated 

 activity of the sweat glands so favors heat escape, that the injuri- 

 ous effect of excessive body heat is prevented. Again, the viscera 

 concerned in digestion (notably the liver) generate much heat; by 

 the blood it is carried to the cooler extremities. 



A high temperature of the surrounding atmosphere so affects 

 the nerve centers, that the respiratory function is stimulated 

 and evaporation from the lungs increased, at the same time 

 activity of the skin is very marked and evaporation of perspiration 

 follows. 



